The proteasome (or macropain) (EC 188.8.131.52) [1,2,3,4,5,6,7] is a multicatalytic
proteinase complex that seems to be involved in an ATP/ubiquitin-dependent
nonlysosomal proteolytic pathway. The core of this 2.5 MDa enzyme complex is
formed by the 20S proteasome, a barrel-shaped protease of about 700 KDa that
associates with one or two 19S regulatory complexes. All archaea and
eukaryotes have a 20S proteasome as well as some actinobacteria , but most
bacteria have a simpler homologous structure heat shock locus v (HslV) or
The main difference between prokaryotic and eukaryotic proteasomes is one of
complexity. Prokaryotic 20S proteasomes contain mostly only to different but
related subunits, α and β (see <PDOC00668>), while eukaryotic
proteasomes contain seven paralogous α-type and seven paralogous β-type
subunits. Subunits that belong to the β-type group are proteins of from 190
to 290 amino acids that share a number of conserved sequence regions. The HslV
subunit has sequence similarity with the β-type subunits of the 20S
Some subunits that are known to belong to this family are listed below:
- Vertebrate subunits C5, β, delta, epsilon, theta (C10-II), LMP2/RING12,
C13 (LMP7/RING10), C7-I and MECL-1.
- Yeast PRE1, PRE2 (PRG1), PRE3, PRE4, PRS3, PUP1 and PUP3.
- Drosophila L(3)73AI.
- Fission yeast pts1.
- Thermoplasma acidophilum β-subunit. In this archaebacteria the
proteasome is composed of only two different subunits.
- Rhodococcus erythropolis 20S proteasome β subunit 1 (PrcB 1) and 2 (PrcB
- Escherichia coli ATP-dependent protease subunit HslV (EC=184.108.40.206).
The proteasome β-type subunit structure consists of a core of two
antiparallel β sheets that is flanked by α helices on both sides (see
As a signature pattern for proteasome B-type subunits we selected the best
conserved region, which is located in the N-terminal part of these proteins.
The pattern is specific for the 20S-subtype and does not detect the HslV-subtype. We also have developed a profile which covers the whole conserved
region of both subtypes.
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